Liquid compositions of (per)fluorinated ion exchange polymers are known for use in the manufacture, and possibly repair, of ion exchange membranes, for membrane coatings containing conductive and non-conductive particles, and for many other uses. While such compositions are sometimes referred to as solutions, the compositions are generally recognized as being dispersions (in other words, colloidal suspensions) of polymer particles.
Liquid compositions are typically prepared by dissolving/suspending in an appropriate aqueous or aqueous-alcoholic medium the (per)fluorinated ion exchange polymer. Methods useful for obtaining such liquid dispersions are notably taught in U.S. Pat. No. 4,433,082 (DUPONT DE NEMOURS) 21 Feb. 1984, GB 1286859 (DU PONT) 23 Aug. 1972, EP 1004615 A (AUSIMONT S.P.A.) 31 May 2000 and U.S. Pat. No. 6,150,426 (DUPONT DE NEMOURS) 21 Nov. 2000.
Nevertheless, said liquid compositions generally suffer of a poor compromise between liquid viscosity, surface tension and solid contents. Actually, it is generally understood that for achieving optimal impregnation of porous support it is important to:                reduce liquid viscosity, so as to maximize penetration ability of the liquid in the porosity of the support and to limit thickness of membrane thereof;        reduce surface tension, so as to increase wettability towards low surface tension supports, usually ePTFE;        increase solids content, so as to maximize coated/impregnated amount of (per)fluoroionomer, remaining in the porous support structure after solvent evaporation.        
Failure to simultaneously comply with all above mentioned requirements in the dispersion typically provides in the eventual impregnation step a porous support with an uneven fluoroionomer distribution.
Typically, in liquid compositions of the prior art, reduction of the surface tension is obtained by addition of polar organic solvents (e.g. alcohols) or surfactants: nevertheless this addition typically gives rise to a simultaneous increase in liquid viscosity, which is detrimental for the impregnation process and which prevents from simultaneous increase of solids, this latter parameter being responsible of further increases in liquid viscosity.
Also, techniques are known according to which (per)fluoroionomers are submitted to particular treatment for improving certain performances, in particular in their fuel cells operations.
Thus, documents US 2008292935 (DU PONT DE NEMOURS) 27 Nov. 2008 and WO 2008/054420 (DU PONT DE NEMOURS) 5 Aug. 2008 disclose a process for manufacturing certain fluoroionomer dispersions comprising, inter alia, fluorinating a fluoroionomer and dispersing said fluorinated fluoroionomer in a water/alcohol mixture, as described in U.S. Pat. No. 4,433,082 (DUPONT DE NEMOURS) 21 Feb. 1984.
Nevertheless, so obtained dispersions fail to provide an improved surface tension/liquid viscosity/solids content compromise and thus are unsuitable for manufacturing composite membranes having a homogenous content of the fluoroionomer through the porous support thickness.